Replaceable printer cartridges tend to be relatively expensive due largely to the fact that they have a fixed ink volume. This ink volume must be relatively small because the cartridge is part of the rapidly moving print carriage, and thus, ink cartridges with larger volumes would require larger and more costly mechanisms for such motion. Larger ink volumes would also lead to more breakdowns of the system due to the increased stress on the components that must support and move the larger ink volume.
To extend the useful life of disposable print cartridges, large-volume and stationary ink reservoirs have been mounted to ink jet printers to refill the ink contained in the print cartridges installed on the moving carriages. But these systems must contend with certain design obstacles. For instance, the pressure of the ink in the cartridge should generally be lower than atmospheric pressure, or relatively negative, in order to prevent ink from running out of the nozzle plate. This means that the cartridge must not only contain the ink, but it must also include a structure or component that lowers the pressure of the ink stored in the cartridge, even when refill ink is being supplied to the cartridge. Also, the rapid movement of the print head can cause pressure fluctuations in the print cartridge. Finally, as previously mentioned the weight of the printer cartridge should be minimized to reduce both the cost and frequency of repairs of the print head support and movement mechanisms.
One attempt to address these issues comprises a system that directly connects the print cartridge to a large-volume reservoir through an ink supply line. Another concept uses a modular approach to achieve the same goal, allowing the replacement of the cartridge or the large-volume ink reservoir independently of one another. These two approaches have disadvantages, however. For example, the hydraulic pressure at the nozzle plate on the print cartridge is affected by the height of the large-volume reservoir, a pressure drop caused by the viscous ink flow in the ink supply line, and pressure surges caused by the carriage acceleration during printing. As mentioned before, these unfavorable pressure effects can adversely impact the performance of the nozzles, hindering printer performance and print quality. In general, the ink droplets expelled from nozzles on the print head become smaller when the pressure inside the printer cartridge becomes more negative. During printing, the pressure variation related to the reservoir height, the viscous flow in the ink supply line and the pressure surges caused by carriage acceleration, therefore, cause print quality to degrade. When the pressure inside the printer cartridge becomes too negative, nozzle starvation can happen, resulting in a failure of the nozzles to stop expelling ink. Other disadvantages of these systems include difficult cartridge replacement procedures that can be very messy.
Other proposed solutions to the problem allow the printer cartridge to regulate its own pressure to minimize the effects of pressure variations from the large-volume reservoir, the pressure loss in the supply line and the surges from printer carriage acceleration. One such system adopts a “take a gulp” method for refilling the printer cartridge. When an ink refill is required, the printer carriage stops at a refill station at one end of the carriage travel and is refilled from the large-volume reservoir. Another approach involves installation of pressure sensing and control devices in the replaceable print cartridge. This system allows on-the-fly ink refill during printing by using a valve, bias spring, and variable volume containment chamber in the cartridge. The valve is adapted to regulate ink flow from a remote reservoir. The ink refill is mechanically controlled by the valve, which is mechanically linked to the containment chamber. When the containment chamber volume decreases to a certain value, the valve is opened to commence the flow of refill ink and to increase the volume of the containment chamber until the volume increases to a certain value at which point the valve closes securing the flow of refill ink. When the print cartridge needs to be replaced, the whole pressure regulation system is disposed of.
Another alternative adopts a different approach; this approach puts the entire pressure regulation system on the printer base and not on the carriage.
In this way, the pressure regulation system is not disposed of when the cartridge is replaced, and the ink refill decision is made by the more powerful printer, which can utilize more information, such as from the large-volume ink reservoir as well as print conditions and history. However, the pressure sensor is not in the print cartridge so the pressure that is regulated is not the cartridge pressure but rather is the refill line pressure, which can be substantially different. All of these approaches attempt to refill the ink in the print cartridge while maintaining the appropriate pressure, at an affordable cost while offering the best performance. These proposed solutions fail to effectively refill the ink in the print cartridge while maintaining the pressure in that cartridge in the most effective manner. What is needed, is a system that utilizes the power of the printer controller to control the refill cycles, to most effectively regulate the refill process. The system should also maintain the correct pressure in the print cartridge while storing the refill ink volume separate from the print head. The system should also limit the amount of components that must be discarded and replaced when the print cartridge is replaced.